In a case of winding one wire rod in line around a bobbin as a tool for winding, for example, a bobbin a winding core of which has a cross section of a square shape, it is general to perform feeding equal to an amount of a wire diameter of a wire rod on one face of the four faces. In this case the feeding is not made in the other three faces.
When a wire rod is wound to an end of the winding core and then moves on an upper layer for the winding thereon, since on the face where the feeding of the wire rod is made, the winding direction of the wire rod in the lower layer is in reverse to that in the upper layer, a hatched portion, as shown in FIG. 13, is an intersection portion where the wire rod in the lower layer intersects the wire rod in the upper layer. On the face (referred to as a wire rod feeding face) where the wire rod in the lower layer thus intersects the wire rod in the upper layer by feeding the wire rod, the wire rods are overlapped in two layers (for example, refer to Japanese Unexamined Patent Publication No. 8-203720). On a face other than the wire rod feeding face, since a groove between the neighboring wire rods serves as a guiding groove of the wire rod in the upper layer, the wire rods do not intersect and are not overlapped.
Next, a case where a set of two wire rods are wound in parallel to each other in line around a bobbin a wiring core of which has a cross section of a square shape will be explained with reference to FIG. 14A. In this case, on the wire rod feeding face as one face of the four faces, the feeding of the wire rods correspond to an amount of two wire rods (arrow 1 in the figure). At the end of the wire rod feeding face, the wire rods are wound in such a way as to move on the upper layer, leaving a clearance equivalent to an amount of 0.5; wire rods (arrow 2 in the figure) In addition, the wire rods in the upper layer are fed by an amount of two wire rods in the opposing direction to the winding direction of the wire rods in the lower layer (arrow 3 in the figure). In the case of thus winding a set of two wire rods in line, there is generated an intersection portion where the wire rods in the lower layer intersect the wire rods in the upper layer.
At this point, a hatched portion shown in FIG. 14A is a state where the wire rods are wound and overlapped to be in three layers. Accordingly, on the feeding face, the bulge in the direction of the outer diameter increases. Similarly also in a case where a set of three wire rods or a set of four wire rods are wound in parallel to each other in line around a bobbin a winding core of which has a square cross section, a hatched portion on the wire rod feeding face, as shown in FIG. 14B or FIG. 14C, is a state where the wire rods are wound and overlapped to be in three layers.